1. Field of the Invention
The invention relates to a laminated composite body, in particular conveyor belt, comprising a support which essentially determines a mechanical stability of the laminated composite body and at least one cover plate made of rubber, thermoplastic elastomer and/or plastics, which has a high resistance to mechanical damage in the form of notches, cuts or the like.
A particularly important example of a laminated composite body according to the invention is a conveyor belt.
2. Description of Related Art
The conveyor belt, as an essential component of belt conveying systems, essentially has to fulfill two tasks. The first task consists in transmitting a belt tensile force, in order to build up sufficient normal forces in the belt between the drive drums to be able to transmit the drive force by means of the friction on the belt. The tensile force for overcoming the kinetic resistance is taken up by the mechanical reinforcement arrangements situated in the belt. The conveyor belt furthermore has to transport material for conveying. The material for conveying is regularly thrown onto the conveyor belt, specifically from a height of up to 10 m. Since the material for conveying may also be sharp-edged rock or the like, the conveyor belt has to be configured such that the impact of the material to be conveyed on the conveyor belt does not lead to any damage to the belt. To this end, the conveyor belt is provided with a cover plate, which in particular has the function of protecting the mechanical reinforcement arrangement in the tension support layer, which serves as support, from damage, since damage of this kind impairs or destroys the operating capacity of the belt. Steel cable arrangements or arrangements of a plurality of layers of fabric are conventional for the reinforcement arrangement.
Due to continuous pelting from the particles of bulk material, the top layer of the cover plate of a conveyor belt becomes scarred during operation, sometimes forming relatively small notches. The notches or scars may become the starting point for slitting or hairline cracks, which propagate as a function of the operating conditions (belt speed, trough of the conveyor belt, spacing of the drive rollers), of the material being conveyed and of the belt properties, as a result of the continuously changing states and concentrations of stresses at the crack tip. This may result in penetration as far as the tension support layer, which places the operating capacity of the conveyor belt in doubt. In practice, therefore, a conveyor belt which is exposed to the bulk material over a relatively long period of time is replaced when the surface of the cover plate exhibits numerous scars and notches due to the continuous impact of the bulk material.
A known measure for increasing the service time consists in increasing the thickness of the cover plate. As a result, the energy required for penetration is increased. However, it is not possible to prevent notches and cuts leading to penetration through even the greater thickness of the cover plate. The effect achieved with the increased use of material is therefore limited.
A further known measure for increasing the service life consists in incorporating transverse reinforcements made of textile or metal materials. The latter have to join to the rubber well and permit the required trough properties of the conveyor belt. The aim of the transverse reinforcement is to cushion high inputs of energy from the falling material in that it absorbs forces itself, distributes the stresses and thus prevents direct penetration onto the tension support layer. Above all, it prevents those longitudinal cuts which may lead to steel cables fanning out. However, this measure does not make it possible to exclude the risk of notches and cuts being formed.
It is furthermore known, in order to increase the service life of belt cover plates, to introduce fibers into the cover plate material. In order that differing properties of the cover plate in the longitudinal and transverse directions should not arise, the distribution of the fibers has to be unoriented. However, conventional processing (calendering) of the cover plate produces a preferred alignment of the fibers, which does not make it possible to construct a closed fiber network. Therefore, the introduction of fibers into the cover plate is also only of limited use.
Another example of a laminated composite body mentioned at the outset is a roller having a cover layer applied on a metallic core, which cover layer is exposed to similar stresses, from granular and sharp-edged material being rolled, to the cover layer of a conveyor belt.
A laminated composite body of the type mentioned at the outset, designed as a conveyor belt, is disclosed by DE-A 17 50 410. In this case, a plurality of layers taking up the tension are provided, the cover plates which close off the layers taking up the tension to the outside being of single-layer construction.
EP 0 431 907 A2 discloses a roller coated with rubber, on the metal core of which are applied two rubber layers, the two rubber layers being formed from essentially the same base material and the outer rubber layer merely having an additive increasing the abrasion resistance, for example in the form of a zinc salt.
A multilayer waterproof sheeting for roofs is known from DE 33 42 560 A1, in which sheeting an EPDM rubber, which is per se advantageous, is provided with a glass fiber reinforcement, but on the outside is covered by an SEBS rubber layer which enhances the usual laying of the waterproof sheeting for roofs. The multilayer structure therefore stems from the usual laying technology for waterproof sheeting for roofs and is not intended to increase the resistance to mechanical damage in the form of notches, cuts or the like.
The same applies to the erosion-resistant and corrosion-resistant protective coating which is disclosed in DE 92 07 785 U1. The latter has an outer antiwear layer having a Shore A hardness of 45 to 75, a soft rubber layer beneath this having a Shore A hardness of 45 to 55, a supporting layer and a fourth layer made of soft rubber having a Shore A hardness of 45 to 75. The supporting layer consists of a layer of steel, a layer of fabric or a layer of hard rubber having a Shore D hardness of about 70 to 80. The corresponding coating is intended to have a high resistance to chemically aggressive materials, which permit sic! use in flue-gas desulfurization plants. Increasing the resistance to mechanical damage in the form of notches, cuts or the like was neither the desired object nor disclosed.